Circuit Description
The control module monitors the fuel tank pressure (FTP) sensor signal in order to detect vacuum decay and excess vacuum during the evaporative emission (EVAP) diagnostic test. The control module supplies a 5-volt reference and a low reference circuit to the FTP sensor. If the control module detects the FTP sensor signal voltage above a calibrated value, this DTC will set.
The following table illustrates the relationship between FTP sensor signal voltage and the EVAP system pressure/vacuum.
FTP Sensor Signal Voltage | Fuel Tank Pressure |
|---|---|
High, Approximately 2.5 Volts or More | Positive Pressure |
Low, Approximately 2.5 Volts or Less | Negative Pressure/Vacuum |
Conditions for Running the DTC
The ignition is ON.
Conditions for Setting the DTC
| • | The FTP sensor voltage is more than 4.75 volts. |
| • | The condition is present for more than 50 seconds. |
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the DTC
| • | A current DTC Last Test Failed clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic. |
| • | Clear the DTC with a scan tool. |
Diagnostic Aids
| Important: A short to B+ on the FTP signal circuit may have damaged the FTP sensor. |
| • | The FTP sensor voltage should be between 2.35-2.85 volts with the ignition ON, the engine OFF and the fuel cap removed. This represents atmospheric pressure, or 0 inches H2O, of vacuum. |
| • | The FTP sensor 5-volt reference circuit is shared with the following sensors: |
| - | The CMP sensor |
| - | The EGR valve |
| - | The MAF sensor |
| - | The MAP sensor |
| - | The A/C pressure sensor |
| - | The APP sensor 1 |
| • | The FTP sensor low reference circuit is shared with the A/C pressure, the fuel level sensor, and the APP sensor 2. |
| • | Inaccurate readings will occur if resistance measurements are taken on an FTP sensor. The FTP sensor contains an internal amplifier circuit that requires applied voltage to function properly. |
| • | To locate an intermittent condition, monitor the FTP sensor voltage with the ignition ON and the engine OFF. Wiggling wires while watching for a change in the FTP sensor voltage may help locate the area where a fault may exist. |
| • | For intermittent conditions, refer to Intermittent Conditions . |
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Engine Control Module Connector End Views | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
2 |
Is the voltage more than the specified value? | 4.75 V | Go to Step 4 | Go to Step 3 |
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids |
4 |
Is the voltage within the specified range? | 4.0-6.0 V | Go to Step 5 | Go to Step 9 |
5 | Measure the amperage from the signal circuit of the FTP sensor to a good ground. Is the amperage below the specified value? | 1 mA | Go to Step 6 | Go to Step 10 |
6 | Measure the voltage from the 5-volt reference circuit of the FTP sensor to a good ground with a DMM. Is the voltage within the specified range? | 4.8-5.5 V | Go to Step 7 | Go to Step 11 |
7 | Measure the voltage from the low reference circuit of the FTP sensor to a good ground. Is the voltage below the specified value? | 1 V | Go to Step 8 | Go to Step 13 |
8 |
Is the resistance less than the specified value? | 100 ohms | Go to Step 14 | Go to Step 12 |
9 | Test the signal circuit of the FTP sensor for a short to voltage or an open between the fuel tank wiring harness connector and the control module. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 16 |
10 | Test the signal circuit of the FTP sensor for a short to the 5-volt reference circuit between the fuel tank wiring harness connector and the control module. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 16 |
11 | Test the 5-volt reference circuit of the FTP sensor for a short to voltage between the fuel tank wiring harness connector and the control module. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 16 |
12 | Test the low reference circuit of the FTP sensor for an open between the fuel tank wiring harness connector and the control module. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 16 |
13 |
Important: A short to B+ on the low reference circuit may have damaged the control module. Repair the low reference circuit of the FTP sensor for a short to voltage between the fuel tank wiring harness connector and the control module. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 19 | -- |
14 |
Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 15 |
15 | Inspect for poor connections at the fuel tank harness connector and the FTP sensor harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 17 |
16 | Inspect for poor connections at the harness connector of the control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 18 |
17 | Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 19 | -- |
18 | Replace the control module. Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 19 | -- |
19 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 20 |
20 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |
